Project Summary The p53 family of tumor suppressors is consisted of p53, p63, and p73. The p53 family proteins act as a tumor suppressor primarily through their transcriptional targets. We and others showed that ferredoxin reductase (FDXR) is induced directly by p53, p63 and p73. Initial investigations showed that ectopic expression of FDXR increases, whereas partial disruption of the FDXR gene decreases, the sensitivity of tumor cells to DNA damage-induced apoptosis in a p53-dependent manner. To investigate the biological function of FDXR, we carried out a pilot study by generating FDXR-deficient cells and mouse models. We showed that FDXR deficiency promotes iron regulatory protein 2 (IRP2) expression. We also showed that cells deficient in FDXR exhibit iron overload in the mitochondria. Most interestingly, we showed that cells deficient in FDXR are also deficient in p53 and p73 expression. In contrast, p63 expression is increased in FDXR-deficient cells. Furthermore, FDXR+/- mice have a short lifespan along with high incidence of spontaneous tumors. These observations prompt us to hypothesize that the FDXR-p53 family pathway is necessary for tumor suppression. To test this, we will determine: (1) how p53 is regulated by FDXR and the role of the FDXR-p53 loop in tumor suppression; (2) how p63 is regulated by FDXR and the role of the FDXR-p63 loop in tumor suppression; (3) how p73 is regulated by FDXR and the role of the FDXR-p73 loop in tumor suppression.